The present invention relates to a novel type of textile reinforcement, based on glass filaments in particular, adapted to be used for making laminated complexes. It also relates to a process for obtaining such a type of reinforcement.
Among the textile materials used for making laminated articles, i.e. articles based on a resin (polyester or other) reinforced by a textile structure, it has been proposed to produce a type of textile reinforcement so-called "unidirectional" layers primarily consisting of fibers (for example glass filaments) extending transversely with respect to the length of the layers, said filaments being bound together by a loose binding warp which maintains the filling yarns parallel to one another.
When making the laminated article, a plurality of layers produced in this way are superposed, offsetting them, for example, by 90.degree. with respect to one another in order to have good mechanical characteristics both lengthwise and widthwise.
It has also been proposed to use textile reinforcements in which the cross yarns are disposed on a bias with respect to the length, such articles being constituted not by a veritable weave but by a "grid", i.e. a structure composed of superposed layers of yarns, oriented differently from one another and bonded together by adhesion. Such articles of the "grid" type make it possible to obtain laminated materials reinforced in all directions, but they present the drawback of comprising a large quantity of binding agents which may be detrimental to the qualities of the finished composite article.
Now, a novel type of unidirectional woven textile material has been found, and forms the subject matter of the present invention, which not only presents the advantages of such woven articles, i.e. a good holding of the yarns with respect to one another, but also offers the possibility, as in the case of the non-woven textile grids, of obtaining unidirectional articles in which the majority yarns extend on a bias with respect to the binding warp yarns, forming any angle with respect to said yarns.
The invention generally relates to a novel type of textile reinforcement adapted to be used for making laminated articles, this reinforcement being of the type constituted for the major part by fibers extending transversely with respect to the length of the layer, said yarns being joined together by a loose binding warp, and is characterized in that:
the transverse yarns are disposed on a bias with respect to the length of the binding warp, and PA0 said binding warp is based on yarns which are at least superficially thermo-fusible.
The material constituting the cross yarns will be composed of any type of conventional material for making laminated articles (such as glass fibers, carbon fibers, aramid fibers such as those marketed under the trademark "KEVLAR").
Furthermore, the fusible yarns for making the binding warp will be constituted by any material compatible with the resins to be reinforced. A yarn based on copolyamide may, for example, be used (such as those marketed under the trademark "GRILON") for which the zone of fusion lies between 70.degree. and 150.degree. C., these yarns being either multifilaments or monofilaments. Core spun yarns may also be used, comprising a core based on a material similar to those of the warp yarn (for example glass, aramid, carbon, . . . ), coated with a layer of thermo-fusible material such as a layer of polyamide or polyester.
When making the laminated article, the layers according to the invention may be superposed, orienting the cross yarns differently from one layer to the other, which makes it possible to obtain reinforcement in all directions. During such a superposition, the presence of the thermo-fusible binding yarns further promotes the bond between the different layers. The different superposed layers may possibly be combined with other textile materials such as non-woven fibrous layers, the stack thus formed being able to be joined by stitching, knitting, etc.
The present invention also relates to a process for obtaining such textile reinforcement, said process consisting of weaving an article comprising filling yarns bound to one another with woven warp yarns which are loose with respect to the density of the filling yarns, being characterized in that, after having made said fabric, the orientation of the filling yarns with respect to the warp yarns is modified and, at the same time, a heat treatment is effected, provoking the superficial fusion of the binding warp yarns.
The displacement of the orientation of the filling yarns with respect to the warp yarns may be obtained by any known means, for example by means of a tentering machine in which the lateral holding elements have a displacement offset with respect to each other.